This invention relates to a method for preparing an electrode for an electrochemical system. More particularly, this invention relates to a two-step chemical activation process for a hydrogen storage-based electrode comprising a metal hydride (MH) for an electrochemical system.
An electrochemical system, such as a fuel cell, is capable of efficient energy conversion and can be used in a variety of applications including transportation applications, portable power sources, home and commercial power generation, large power generation and any other applications that would benefit from the use of such a system. Fuel cell systems may be fueled with pure hydrogen and emit only water and energy in the form of electric power and heat. A battery can also be a source of energy that is limited to the stored energy it holds. A fuel cell is capable of generating energy as long as a fuel is supplied.
In a fuel cell device, hydrogen is supplied to the anode or stored within the anode while an oxidant is supplied to the cathode. Hydrogen can also be stored at the negative electrode of a battery. For example, metal hydrides are commonly used as a material for the negative electrode of batteries, such as air-metal hydride batteries and Ni-metal hydride batteries, or for the anode of solid-state hydrogen storage-based fuel cells. Metal hydride materials or electrodes comprising metal hydrides need to be activated before being integrated with cathodes and other components to form the batteries or the fuel cells. This is necessary because the untreated metal hydrides may form an oxide layer on the surface of the metal hydride leading to poor charging efficiency and low discharge capacity. An activation process is essential to remove the oxide layer from the surface of the metal hydride. Furthermore, in the absence of an activation process, additional electrochemical charge-discharge cycles are needed to reach the maximum storage capacity of the metal hydride material and the initial discharge capacity is too low to run the electrochemical system efficiently.
There are several processes that are used to prevent oxide formation on the surface of the metal hydride or to activate the metal hydride material such as metal or alloy coating, hot alkali treatment, acid treatment, and chemical reduction method using reductants in alkali solution. Generally, these methods are employed to treat the metal hydride powder. Further activation of the anode or the negative electrode comprising the metal hydride powder is not done if the powder itself is activated through an activation process. Similarly when the fabricated negative electrode or anode comprising the metal hydride powder is treated in an activation process after the fabrication, the activation process of the metal hydride powder itself is not practiced.
Therefore there is a need for an efficient activation process to activate the hydrogen storage based electrodes comprising metal hydrides in electrochemical systems.